1. Field of the Invention
This invention relates to a control system for preventing an aircraft colliding with designated man-made structures.
2. Description of the Related Art
It is widely appreciated that aircraft, particularly civil passenger aircraft, are at risk of being commandeered by unauthorised people. Recent events have shown that aircraft pilots can be overpowered and unauthorised people can fly civil aircraft into buildings with great loss of life.
A flight control system is known. U.S. Pat. No. 5,488,563 (Chazelle et al.), which compares the position of an aircraft as determined by a Global Positioning System (GPS) or the like with a detailed map of the terrain over which the aircraft is expected to fly. With this information the system can alert a pilot if the aircraft appears to be on a ground collision course. However, this type of system requires a very large database detailing all topographical data proximal the flight-path, much of which is irrelevant. Such systems do not address the situation where an aircraft legitimately needs to fly near man-made structures such as buildings; for example, during landing at an airport.
Aircraft flight controls systems, such as autopilots, are many and well known; they shall not be described here to maintain conciseness. The applicant refers the reader to many publications in the name of Boeing R™ and others; for example, U.S. Pat. No. 4,644,538 (Cooper et al.) that describes a general autopilot system, and U.S. Pat. No. 5,868,659 (Cartmell et al.) that describes an autopilot system for use with a fly-by-wire aircraft control system.
During flight, passenger airliners frequently fly on autopilot. While it is possible for access to such autopilot systems to be protected by passwords etc., to avoid unauthorised access such security has its limitations. Threats can persuade pilots to unlock such systems, and ultimately the aircraft normally needs to return to manual control before landing.
There is also an urgent need to protect designated man-made structures and sites that are thought likely to be attractive targets for pilots who wish to deliberately crash an aircraft. For example; such sites may be buildings in which thousands of people work; sites of national and international importance, such key economic and historic buildings; military and governmental installations; and hazardous processing or production sites. Such sites can be protected by surface to air missile (SAM) systems but such systems present great potential danger, especially to aircraft passengers. Further, stationing SAM systems at all such sites is costly and impractical and, indeed, represents a potential additional security threat. There are also situations where such systems may not be able operate sufficiently quickly, even if activated automatically; for example, where a legitimate flight path passes close to a potential target; especially during aircraft approach to or departure from a civil airport. In such cases deviation from the correct flight-path for just a few seconds may be sufficient to result in a catastrophic collision.